msm: vidc: Code clean up

Clean up the code base by deleting useless variables and renaming
structs (and their respective members) to be more consistent with driver
conventions.

Change-Id: I79efade0f10b0e2e955da2147b7c0b2c9cb42b04
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>